Pipetting systems are used in laboratories for the transfer of relatively small quantities of liquids. The liquid is normally drawn into the tips by suction and is subsequently released into the wells of microtiter plates or other receptacles. Frequently the transfer involves patient samples which are moved from one set of spaced receptacles to another set of receptacles having a different spacing. A multi-channel pipettor capable of being simply manipulated to vary the spacing between the pipette tips is often used for this purpose. Typically, the pipettor has a tip removing assembly that, with a minimum of force, removes tips safely and efficiently regardless of the positions of the tips and their fittings on the pipettor. One shortcoming of some prior art pipettors is that the pipette tips can only be adjusted between two uniform standard spacings of the receptacles. The standard settings must be preselected prior to manufacture. An example of such a prior art structure is found in U.S. Pat. No. 5,061,449.
A second type of multi-channel pipettor, such as that shown in U.S. Pat. No. 5,057,281, allows the spacings between the tip fittings to be varied by the user. However, the spacings between each fitting must be individually set. Thus, considerable manipulation is required to move the tip fittings from one set of spacings to another and it is difficult to accurately set the tip fittings to the desired spacings.
Therefore, it is desirable to have a multi-channel pipettor in which the tip fittings may be quickly and accurately set at a variety of uniform spacings. Moreover, it is desirable to easily vary the spacings while maintaining uniform spacing between tip fittings.